1. Field of the Invention
The present invention relates to an operating circuit arrangement for a discharge lamp. More specifically, the present invention relates to an improved operating circuit arrangement for a fluorescent lamp, which includes at least a chopper circuit and an inverter circuit.
2. Description of the Related Art
An operating circuit arrangement for a discharge lamp formed with a chopper circuit, an inverter circuit and a lighting circuit is well known. The inverter circuit inverts a d.c. voltage to a high frequency voltage and supplies it to the lighting circuit. The d.c. voltage is generated by the chopper circuit where it is then supplied to the inverter circuit. A discharge lamp adapted to the lighting circuit is operated in response to the high frequency voltage. By the operation of the chopper circuit which supplies a substantially constant d.c. voltage to the inverter circuit without lowering the power factor and distorting the output current, the lamp efficiency is increased. The chopper circuit is provided with a chopper control circuit, which controls a driving frequency of a Field Effect Transistor (FET) used as the chopping means in order to generate a given d.c. output voltage. Operation of a separately-excited oscillation type invertor circuit is controlled by an inverter control circuit. Each of the control circuits are provided with specific power source circuits. This is disadvantageous in view of power consumption because the power consumption is continued at the chopper circuit even after the extinction of the discharge lamp. Japanese Patent Disclosure (Kokai) 62-77860 discloses an operating circuit arrangement for a fluorescent lamp, which comprises a chopper circuit, an inverter circuit and a chopper output control circuit. In the Kokai disclosure, an output derived from a secondary winding provided in the inverter circuit is fed to the chopper output control circuit and is regarded as a power source for the chopper output control circuit. However, this output is dependent on the operating condition of the inverter circuit. Namely, the output is not constant. This is disadvantageous for the operating circuit arrangement.
Generally, a conventional inverter circuit is designed to start its operation when the output of the chopper circuit exceeds a given value. As long as the output of the chopper circuit is lower than the given value, the discharge is held in an off-state circuit is regarded as a no-loaded condition. When the operating condition is changed from a no-load condition to a loaded condition, a high output voltage is applied to a switching device of the inverter circuit, which can damage the switching device. This is also disadvantageous for the operating circuit arrangement for the discharge lamp.